Windmills have been in use throughout the world for generations harnessing the power of the wind. The windmill performs functions such as pumping water or grinding flour. A wind turbine is a windmill that converts the energy of the wind into a viable source of electrical power.
In an existing wind turbine, the shaft of the turbine is connected to a generator located in the nacelle of the wind turbine. The generator is in turn connected to a high voltage transformer, typically located at the base of the tower of wind turbine. The high voltage transformer is connected to the generator by cables which are located in the tower. The high voltage transformer converts the electrical power from the generator into higher voltages. The output from the high voltage transformer is then connected directly into a utility's power grid.
A source of 120/240V AC power at the nacelle of the wind turbine is beneficial because it gives the utility company the ability to provide lighting to assist maintenance personnel. Additionally, this 120/240V AC power source allows the utility company to change the pitch of the turbine blades even though the turbine is not generating electricity. One way to provide such an AC power source is to connect a separate low voltage transformer to the output of the generator. The low voltage transformer taps off the connection between the generator and the primary winding of the high voltage transformer. With this connection, the low voltage transformer provides 120/240V AC power when the generator is generating electricity and when the generator is not on line as long as the high voltage transformer remains connected to the power grid. By back feeding the low voltage transformer from the power grid, 120/240V AC power is available to assist the craftsperson during wind turbine maintenance periods.
In another wind turbine design, the high voltage transformer is located in the nacelle and there is no low voltage transformer. A craftsperson would have to bring a portable generator in order to provide a 120/240V AC power when performing work at the tower. The generator would have to be located at the base of the tower in a well vented location.
In yet another wind turbine design, the generator and high voltage transformer are located in the nacelle of the turbine and a separate low voltage transformer is located at the bottom of the tower. In this design, low voltage wires are run from the connection between the generator and the primary side of the high voltage transformer to the low voltage transformer. High voltage wires in the tower connect the high voltage transformer to the power grid. Locating the high voltage transformer in the nacelle of the turbine creates some difficulties. Typically, the ability to take the high voltage transformer off line is performed by operating a switch at the high voltage transformer. When the transformer is in the nacelle of the wind turbine, this switching function must remain at or near the base of the tower to allow the utility company to easily disconnect the transformer from the power grid.
When the high voltage transformer is energized, the high voltage wires in the tower of the wind turbine are also energized. These energized cables create a potential risk of electrocution to utility personnel who may be present in the tower of the wind turbine. As a result, when the utility company requires maintenance to be performed at the tower, the high voltage transformer is disconnected from the grid. By disconnecting the high voltage transformer from the grid, any low voltage transformer that is connected between the generator and the primary winding of the high voltage transformer is disabled. With the low voltage transformer disabled, there is no 120/240V AC power for the nacelle.
The present invention is designed to overcome these limitations as well as provide a cost effective solution to isolate and protect the turbine's high voltage transformer when the high voltage transformer is connected into the utility company's power grid.